Power Analysis 2

[signor2004]

A switchgear/MCC has 2 motors or pumps rated 28.26kW (3-phase) and 13.42KW (1-phase). How do I calculate for the total current in order to size the main circuit breaker or fuse in the main supply to the switchgear?

 

[rbulsara]

Review NEC article 430. This forum is not there to do the work for you. This is very well addressed by NEC.

Assuming you are in USA or NEC world. If not refer to similar IEC code.

 

[NewfieSparky]

We are going to need to know the voltage to get the current.
Basically use this formuala:

for 3 phase:
KVA Rating/(SQRT(3)*Voltage)=Current

For 1 Phase:
KVA/Voltage = Current

For you KVA = KW when using unity power factor. The single phase load is only going to increase the current draw in one phase of your 3phase supply. Add it to the 3-Phase current and size your breaker at about 20%-25% greater than this number.

 

[davidbeach]

MCC bus is usually 600A or more. Sizing a feed to an MCC for only the loads listed is usually very short sighted. Size you feeder much closer to the MCC rating.